Cathode ray tube vessel



April 1, 1941. w. H. GRIMDITCH CATHODE RAY TUBE VESSEL Filed May 20,1939 2 Sheets-Sheet 1 Ap 1941- w. H. GRIMDITCH CATHODE RAY TUBE VESSELFiled May 20, 1939 2 Sheets-Sheet 2 i Ax x Patented Apr. 1', 1941 canonsan ma Vassar.

William H. Grimdi lllia'nor, b1

meme assignment z 'to fm%io and Tel vision Corporation, ration ofDelaware Philadelphia, Pa a corpo- Application May :0, 1939, Serial No.274,195

2 Claims. (01. 2515164) This invention relates to a novel vessel orenvelope structure which is particularly adapted for use in cathode raytubes or the like. More particularly, the invention relates to a vesselor envelope structure adapted to be used as a picture tube in electronictelevision for the reproduction of a televised scene upon a screen offluorescent material.

The principal object of the present invention, therefore; is to provideanovel vessel or envelope structure for .use in cathode ray tubes and thelike and particularly for use as a picture tube in television, whichstructure possesses certain advantages over those previously used. asdescribed hereinafter. g

A more specific object of the invention is to provide a novel vessel orenvelope for the abovementioned purposes, which has a fiat endconstituting the viewing screen and which, by virtue of thisconstruction, eliminates the distortion inherent in prior dome endvessels employed heretofore in television picture tubes, and has otheradvantages to be enumerated later.

A still further object of the invention is to provide a relatively thickblank of vitreous material having substantially plane parallel surfacesfor forming the viewing screen of a television picture tube vessel, andwhich is capable of being sealed to the main portion of the vessel whichconsists of relatively thin vitreous material.

The invention may be clearly understood from the following descriptionand accompanying drawings in which:

Fig. 1 is a perspective view of a vessel-or envelope constructedaccording to the invention:

Fig. 2 is a part elevation and part sectional view of the same device;

Fig. 3 is a perspectivelview showing one end of a vessel whichrepresents a preferred form of th invention;

Fig. 4 is a sectional view of the same portion of the vessel orenvelope. taken longitudinally thereof; and

Fig. 5 is a sectional view taken along line 5-5 of Fig. 4.

Referring first to Figs. 1 and 2,-the vessel comprises essentially twoparts A and B the line of division between the two being designated C.Both of these parts are preferably made from some vitreous material,such as glass. and part A is preferably either transparent ortranslucent. In the finished vessel the two parts may be so sealedtogether at C that practically no evidence of the sealing processremains and the two parts appear as one except perhaps for a slightbulgeproduced when the glass is heated.

The partB 'may be of substantially frustoconical form or may be of theform illustrated which is more properly termed a surface of revolution.For the purpose of this specification the term frusto-conical" will beused in a broad sense to designate any surface of revolution with anincreasing cross-section perpendicular to its axis of symmetry. Thesmall end of this frustoconical portion may converge into section Dwhich'may comprise a substantially tubular stem portion, to the end ofwhich may be affixed a cap or base provided with means E for makingconnections to the various electrodes to be contained in the vessel. Ingeneral, the size of the cylindrical stem D will be governed by thespace requirements for the placing and securing of electron guns andother electrodes.

It willbe noted that the thickness of the wall of part Bincreasesslightly as the overall crosssectlon ofthe frusto-conical portionincreases. This may obtain naturally, when the vessel is formed ofglass,

part B with its large end downward, so thatthe hot glass is urgeddownward by the force of gravity and thus tends to make the bottomportion of B thicker than the upper portion adjacent the stem. This isfrequently desirable since, the sur-- face area of the large portionbeing greater, the total pressure thereon and consequently the stress towhich the glass is subjected, is greater. The thicker glass in thisportion makes it better able to withstand the pressure.

The part A of the vessel consists of a disc or blank of vitreousmaterial which is separately cast or molded, and which is later sealedto the frusto-conical portion B. It is this blank which forms theend-viewing screen for the television tube, and on it may be deposited acoating of fluorescent material which, when scanned by an electron beam,eflects the formation of a picture or image. This part of the vesselrepresents an important feature of the invention and presents numerousadvantages not found in prior structures. The end viewing-screen Aconsists essentially of a blank of vitreous material which is flat overthe entirety of its useful surface, by

which is simply meant theentire portion of its external-surface uponwhicha usable image may be produced by the scanning action of a cathoderay beam within the vessel. The inner surface of this blank ispreferably flat outer face, or it may be so formed as to increase thestrength of the end portion of the vessel. In

as a consequence of blowing the and parallel to'the general, however,the principal consideration will be the ability of the screen to permitan image to be viewed which is substantially free from distortion causedby refraction in the medium of which thescreen is formed. and for thispurpose it has been found that parallel surfaces are quite satisfactory.

In an end viewing screen-such as theone herein disclosed, in which theouter surface is entirely flat, it is necessary to thicken the glassconsiderably by comparison with that in the conventional round-ended ordome-shaped tube of the prior art, in which the thickness of the glassin the end viewing screen was substantially the same as that forming theremainder of the vessel.

This increased thicknessof the flat end viewing screen is necessary toobtain a degree of strength comparable to that of the prior dome-shapeding of the corners, the eye tendsto follow the picture as it moves oi!the sides-oi the screen, be-

structure. The necessity for this may be readily Y seen when it isconsidered that in a vessel having a screen diameter of nine inches, thepressure on the screen when the vessel is evacuated is equal toatmospheric pressure multiplied by the area of the screen orapproximately 900 pounds. The increased thickness of the screen,however,.ig not objectionable, and the .results obtained are farsuperior to those obtained when the conventional,

tube with a dome-shaped end is used.. The reason for this isthat withthe dome-shaped vessel,

unless the eye of the observer is positioned-almost on a line with theaxis of, the vessel the straight lines .of the picture televised will bedistorted into curves whose radii will be dependent upon the curvatureof the tube face. Such dis-- tortion is avoided when the present flatviewing screen is employed, and a muchmore pleasing picture is obtainedthan has been possible heretofore.

In practice it was found impossible to seal a" thick blank of glass tothe relativelythin sides of the. main portion of the picture tube vesselwithout the application of heat so intense asto melt the portion of theglass forming the viewing screen, thereby rendering it ineffect veinthis capacity. In ordereto obtain a satisfactory seal, it

was foundnecessary to-reduce the-edges ofthe blank gradually tosubstantially the same thick- .ness as the glass of which thefrusto-conical portion is made. Hence, in accordance with the inventionthis is done by forming around the edge of the blank. a rim sectionas'shown, which pro-v jects substantially at right angles to the mainbody of the blank, which rim is tapered gradually pref erably bothinternally and externally to approximately the thickness of the mainportion of the vessel. Both internal and external tapering are resortedto, as shown in the drawings, as this facilitates the casting of theblank. Further it is desirable for the same reason to slightly chamferor round the corners formed by the intersection of the rim portion withthe main body of the blank. However this chamfering should not be suchas to appreciably encroach on the flat surface of the viewing screen andthereby interfere with the picture. In addition to the advantage alreadypointed out, namely that the flat endedvessel gives a -'tages over theone cause the picture is still visible though tosome extent distorted.This tires the observer-and consequently reduces the entertainment valueof the picture, In thevessel of the present invention. the possibilityoffollowing the picture of! the screen? is precluded by continuing theflat sur-. face of the tubeup to thevery point at which it changesabruptly in such fashionthat the picture gether" at the edges of thescreen.

. Still another advantage of the present structure .is the ease withwhich the flat surfaces of the viewing screen blank may be'ground andpol- 1 ished in large scale production ascompared with.

the priondome-shaped tubes.- In constructing the vessel, theparts A andB are formed separately and then joined together,

as willbe understood-from the-foregoing description. As mentioned above,the part B may be formed by blowing, and the end of the blown part maybe removed'and discarded to form an opengeneral form as the onepreviously described, having faces which are. quite flat, a rim portionwhich tapers to l in the frusto-conical portion of the vessel, andchamfers at the lines oi. intersection between the end blank proper andits rim. The onlydifferenceresides in the shape of the end area which isgenerally rectangular with convex sides. This permits the frusto-conicalportion B to be appreciably flattened so as to give it a cross sectionwhich is generallyrectangular. It is to benoted, however, that thesidesare made convex (see Fig, 5) in order more readily tov withstandthe pressure of the atmosphere to which the vessel is sub- :Iected uponevacuation. i

This form of thevessel presents certain advannrst described in that itwill the cabinet in which the television receiver and other associatedequipment are installed, andit also presents less volume to be evacuatedwhile still giving a viewing screen ofthe desired size and shapetoaccommodate the standard television picture. This latter feature is ofconsiderable importance, of course, from the point of view of increasingcommercial production-when the vessels are evacuated.

It will, of course, he understood that the inven- OCCIIDY 1883 space intion is not limited to the particular forms illusconsiderable reductionin picture distortion, it is also to be noted that any tendency of thepicture to creep around the side of the tube due to overdeflection ofthe electron beam, as is the case with the prior tubes with dome shapedends, is avoided. This is a psychological phenomenon which may beobserved in a person watching a picture on theconventional tube. Becauseof the gradual roundtrated, it being obvious that other specific formsare possible within the scope of the invention as definedwby theappended claims. i

I claim:

l. A vessel or envelope for a television picture tube. comprising agenerally frusto-conical body portion having relatively thin wallsterminating at the large end thereof in a substantially annular edge,and a relatively thick disc having substantially parallel plane surfacesattached to said edge and constituting a picture screen on which portionof the vessel are shown, since the stem portion is of the samesubstantially the thickness of the glass an image may be formed, saiddisc having an in- V tegral annular rim of a diameternot exceeding thediameter of said disc and extending from the edge of the disc in adirection normal to the plane of said disc, at least one wall of saidrim tapering 5 gradually and uniformly from the edge of the disctowardthe outer end of said rim to provide a rim having an appreciablethickness adjacent the disc and a lesser thickness at its outer edge,the outer edge of said rimbeing substantially equal in ex- '10 tent andin thickness to the annular edge at the large endof the body portion,the edge of said rim abutting and being joined to' the edge at the largeend of the body portion, whereby said rim merges into the wall of saidbody portion.

2. A vessel or envelope for a television picture tube, comprising agenerally irusto-conical body portion having relatively thin wallsterminating at the large end thereof in a substantially annular edge,

v at its outer edge,

and a relatively thick disc having sub- 20 stantially parallel planesurfaces attached to said edgeand constituting a picture vscreen 'onwhich an image may be formed, said disc having an integraLtapered,annular rim of a diameter not exceeding the diameter of said disc-andextending from the edge of the disc in a direction normal to the planeof said disc, the inner and outer walls of said rimtapering rg ually anduniformly to ward each other and toward the outer end of said rim toprovide a rim having an appreciable thickness adjacent the disc and alesser thickness the outer edge of said rim being substantially equal inextent and in thickness to the annular edge at the large end of the bodyportion, the edge of saidrim abutting and being joined to the edge atthe large end of the body portion, whereby said rim merges into the walloi said body portion.

mam r1 GRIMDITCH.

